Cross-species matings

In a few science fiction series (the Star Trek franchise being the most notable), humans can mate with extra-terrestrial species and produce healthy children. This is, of course, absolutely ridiculous; species are defined by their inability to mate and produce fertile offspring with other species. Even taking into account the possibility of panspermia, a human would have more in common genetically with a daylily than with an extra-terrestrial.

Cross-species mating in Star Trek

In the Star Trek universe, Humans, Klingons, Vulcans, Romulans, and Cardassians are all cousins whose ancestors were deliberately sown across the galaxy, and can interbreed just as lions and tigers (or dogs and wolves) can on Earth, despite massive physiological (Klingons have two hearts) or biochemical (Vulcans have copper-based blood) differences. Because of Hodgkin's Law, not only Trek species but entire Trek cultures developed along similar paths. Notable products of cross-species matings include: